The present disclosure relates generally to turbine blades and particularly to turbine blade construction.
Many gas turbines, as may be used for power generation and aircraft propulsion for example, utilize turbine blades that are manufactured by a single crystal casting process. A benefit of the single crystal casting process is that it can improve resistance of the turbine blade to low cycle fatigue that may be encountered during turbine operation.
In a power generation turbine, it is desirable to increase the span or length of the turbine blade or airfoil to allow for increased work output per blade to provide for increased power generation needs. The competitive figure-of-merit for increased output in terms of either increased turbine annulus area or mechanical speed is AN2, where A represents the turbine annulus area and N represents the turbine speed. The airfoil span can be extended by a change in foundry practice to larger volume castings. Increasing the casting volume will also increase challenges associated with single crystal processing. These challenges include additional shrinkage, development effort and cost, and capacity constraints of currently available equipment.
Accordingly, there is a need in the art for a turbine airfoil arrangement that overcomes these drawbacks.